AN ORTHOTROPIC DUCTILE DAMAGE MODEL FOR VISCOPLASTIC MATERIALS

Numerical modelling of bulk forming processes has to identify the cond itions that may result in unsatisfactory products. In ductile material s, damage may occur with the micro void nucleation at the site of seco nd phase particles and inclusions in the plastic or viscoplastic matri x and then with the micro void growth. In this work an isotropic ducti le damage model is extended to load cases with successive tensile and compressive steps and with pure deviatoric stress state. The constitut ive equations satisfy the Clausius-Duhem inequality for negative or po sitive voids volume fraction rate. The constitutive parameters are ide ntified with the Rice and Tracey model modified for a sphere initially filled with a soft or a hard inclusion. Axisymmetric geometries are c onsidered for remote strain fields without distortion. A plane cell an d a 3D unit cell are analysed numerically for the deviatoric strain st ate and various combined deviatoric and volumetric deformations.